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We analyze kink and power saturation phenomena of high power 660-nm laser diodes for DVD-R/RW experimentally. Power-current (P-I) and voltage-current (V-I) characteristics of laser diodes with different cavity lengths were measured. Using these results and thermal resistances, temperature rises caused by self-heating (ΔT) and the dependence of slope efficiencies on the temperature rise (Se-ΔT) were calculated. The slope efficiencies decreased linearly with ΔT and their gradients showed the same value regardless of the cavity length, while they had no systematic dependence on the current. The kinks occurred at the same ΔT of 30°C regardless of the cavity length, while they occurred at different currents. These results indicate that the temperature rise caused by the self-heating is a key parameter for the kink and the saturation power. A method is proposed to calculate the kink and the saturation power using the gradient (Se-ΔT) and the kink temperature.